any website through which I can clear doubts in physics and chemistry O level examination past questions?

Answer 1

Try educational sites like dmoz.

Answer 2

relies upon on the instructor. back in severe college Physics exchange into my well known concern on a similar time as chemistry exchange into my least well known. yet when I entered college my Physics professor bored me to dying and notably much each physique interior the class failed. Then I had a chemistry concern the place i myself had an excellent professor. through fact that then i hit upon chemistry less difficult.